There are numerous proposals to transition from the current fossil fuel-based transportation systems to what is known as the “hydrogen economy.” A hydrogen economy would use vehicles powered by fuel cells, or hydrogen-burning internal combustion engines (ICEs), in place of gasoline- or diesel-powered vehicles. However, several problems must be overcome in order to make a hydrogen economy economically and technically feasible. One problem is a lack of an economically viable means of supplying fuel cell-quality hydrogen. Typical fuel cells require a relatively pure form of hydrogen, which makes the hydrogen production more difficult and costly. Another problem relates to hydrogen storage and transportation. To make a hydrogen-powered vehicle practical, hydrogen is stored in one or more tanks under high-pressure. Because of its small molecular size, hydrogen is much more difficult and expensive to compress than natural gas, for example. Typical prior art hydrogen production techniques require the costly step of pressurizing the hydrogen after it is produced.
When a hydrogen-powered vehicle is supplied with fuel, there are two basic options. A first supply option is on-board vehicle extraction of hydrogen from hydrocarbon fuels. A second option is on-board vehicle storage of hydrogen produced and dispensed at a stationary facility. Within these two basic options, numerous specific variations are being studied and/or developed, including, but not limited to, 1) on-board vehicle extraction of hydrogen from gasoline, diesel fuel, naphtha, and methanol; 2) fuel station site hydrogen production via steam methane (natural gas) reforming (SMR) or other hydrocarbon-based processes; 3) fuel station site hydrogen production via electrolysis of water; 4) centrally produced (via large-scale SMR, electrolysis, and other processes) hydrogen delivered to a fuel station by truck or pipeline; and 5) other supply scenarios involving hydrogen production via photochemical, gasification, nuclear, biomass-based, biological, and solar-powered, wind-powered, and hydro-powered methods.
SMR is the most common and least expensive prior art method of hydrogen production, accounting for about 95% of the hydrogen produced in the United States. In SMR, methane is reacted with steam to produce a mixture of hydrogen, carbon dioxide, carbon monoxide, and water, and the mixture is separated to yield high-purity hydrogen. Because of its status as a mature, reliable, economically viable technology, major industrial companies are developing hydrogen vehicle refueling station concepts based on the use of on-site SMR. These concepts involve scaling the process down significantly from its most common commercial application of producing hydrogen at petroleum refineries for use in making cleaner-burning gasoline. Challenges associated with on-site hydrogen generation derive from the unpredictable demands of vehicle fueling. Because SMR works best at a steady-state, 24-hours-a-day, full-capacity operation, integration with a hydrogen fuel station will require costly on-site hydrogen compression and storage (as a gas, a liquid, or in a chemical compound) to compensate for fluctuating hydrogen demand. None of the hydrogen storage technologies available today represents an ideal combination of economy, performance, durability, and safety.
Various prior art methods are available for producing a useful gas or for generating gases from the process of breaking down waste products. For example, as mentioned above, SMR is the most common prior art method of producing hydrogen. Typically, SMR is performed at temperatures in the range of 700°-1000° C. and at pressures in the range of 30-735 psi. Processes that require a high temperature are less desirable since more energy is expended during the process. Similarly, typical prior art processes that produce hydrogen have the disadvantage of requiring pressurization after the hydrogen is produced, since vehicle-fuel hydrogen must be compressed to enable sufficient fuel for a desirable range (e.g., 300 miles).
It can be seen that there is a need for techniques for producing hydrogen on-demand in an economical manner. There is also a need for techniques that produce hydrogen at high pressures, reducing or eliminating the need for the costly step of pressurizing hydrogen after it is produced.